It has long been desired to provide an economical and easily portable apparatus for desalinating and purifying sea water, and which is capable for use in providing an emergency supply of drinking water for sailors, airline crash survivors and oil rig workers who are stranded in life boats, survival suits and the like.
Conventional apparatus used in sea water desalination operate on the principle of reverse osmosis. Reverse osmosis desalinators operate by the user pumping sea water through a membrane which selectively filters sodium and chloride ions from the water. Examples of such reverse osmosis desalinators are disclosed in U.S. Pat. No. 4,161,445 to Coillet, issued Jul. 17, 1979, and U.S. Pat. No. 5,082,564 to Helff, issued Jan. 21, 1992.
A further constraint of reverse osmosis desalinators is that the reverse osmosis technology requires complex manufacturing, making such desalinators prohibitively expensive to most small boat operators and yachtsmen. The high cost of conventional reverse osmosis desalinators make them prohibitively expensive for individual use, as for example packaged in individual survival gear.
The membranes used in reverse osmosis desalinators must be manufactured sufficiently thin to enable the selective transmittal of water, making reverse osmosis desalinators very fragile and succeptible to damage and failure. Reverse osmosis desalinators are not fail-safe, as if the membrane does fail, potable water may not be produced at all.
A major disadvantage of reverse osmosis desalinators is that they are impractical for use in all survival situations. The requirement of a pump mechanism makes conventional desalinators too large to be packaged as part of a life jacket or survival suit. Reverse osmosis desalinators suffer the limitation therefore that they are typically only used in conjunction with life rafts and boats.
While chemical desalinators have been proposed, such as that disclosed in Canadian Patent No. 1,064,630 to Doumas et al, issued Oct. 16, 1979, heretofore the purification of sea water by chemical means has been largely unsuccessful.
The chemical desalinator disclosed in C.P. 1,064,630 incorporates as part of an "ion exchange resin bed" a silver nitrate salt absorbed or impregnated on activated charcoal. The silver nitrate salt provides a source of free silver ions for use in killing bacteria. As a salt is provided which introduces free silver ions, there is also necessitated an ion exchange resin which removes the introduced free silver ions, as ingestion of free silver ions itself could be harmful to the user.
Studies of the effectiveness of the purification of sea water treated with silver nitrate salt "briquettes" show that conventional chemical desalinators produce treated water which may have a pH as high as 11.0. Known chemical desalinators suffer the further disadvantage that they are largely ineffective at removing chloride ions as well as other potentially harmful ions which are found in sea water, such as sulphate (SO.sub.4.sup.=), phosphate (HPO.sub.4.sup.=), potassium (K.sup.+), calcium (Ca.sup.+2) and magnesium (Mg.sup.+2) ions, and the treated water produced after conventional chemical treatment is frequently both muddy brown in colour, and frequently exhibits an unpleasant odour.